1. Field of the Invention
The present invention relates to a color management apparatus and color management system to accurately control colors in a still image system or moving image system, which consists of image capturing using a still camera, video camera and scanner, etc., image transmission using the Internet or dedicated line, etc. and image display using a display, printer, etc.
2. Description of the Related Art
With the progress of digitalization of image processing apparatuses and network technologies centered on the Internet, a cross media system whereby a variety of image processing apparatuses are connected on an open system is becoming widespread on a full scale in recent years. An open system requires individual image processing apparatuses and applications to have a common interface and adopt a configuration with high-level versatility and expandability. From the standpoint of color reproduction, an image processing apparatus that transmits color information, that is, a camera or scanner needs to accurately deliver captured color information to the open system. On the other hand, an image processing apparatus that receives and displays color information, that is, a display or printer, needs to accurately display the color information received. For example, even if a camera acquires color information accurately, color reproduction of the overall system deteriorates with inappropriate color information shown on a display.
Accurate color management among a plurality of image processing apparatuses is becoming commercially practical with the emergence of an ICC profile recommended by the ICC (International Color Consortium). For example, Tim Kohler proposes a next-generation color management method, which also takes into account differences in a visual environment as an expansion of the ICC profile in “The Next Generation of Color Management System (8 th IS&T/SID Color Imaging Conference, P61 to p64)”. On the other hand, there is also a proposal of a mode not limited to an ICC profile. For example, the Unexamined Japanese Patent Publication No. HEI 11-85952 discloses a color management apparatus capable of realizing accurate color reproduction even if illumination on the image capturing side (color information transmitting side) differs from illumination on the observing side (color information receiving side).
Furthermore, accurate color control among a plurality of image processing apparatuses requires a colorimetric value XYZ, which is an objective scale of color. Calculating the colorimetric value XYZ as the objective scale of color requires spectral reflectance Rλ, color matching function (x′λ, Y′λ, z′λ) and spectral distribution Eλ of illumination of an object as shown in (Mathematical expression 1).
[Mathematical Expression 1]
                              [                                                    X                                                                    Y                                                                    Z                                              ]                =                  [                                                                                          ∑                    λ                                    ⁢                                                            R                      λ                                        ⁢                                          E                      λ                                        ⁢                                          x                      λ                      ′                                        ⁢                    d                    ⁢                                                                                  ⁢                    λ                                                                                                                                            ∑                    λ                                    ⁢                                                            R                      λ                                        ⁢                                          E                      λ                                        ⁢                                          y                      λ                      ′                                        ⁢                    d                    ⁢                                                                                  ⁢                    λ                                                                                                                                            ∑                    λ                                    ⁢                                                            R                      λ                                        ⁢                                          E                      λ                                        ⁢                                          z                      λ                      ′                                        ⁢                    d                    ⁢                                                                                  ⁢                    λ                                                                                ]                                    (        1        )            
Therefore, when the image capturing side estimates spectral reflectance of the object and transmits this to the observing side and XYZ is calculated according to the spectral distribution of illumination on the observing side, it is possible to absorb differences in illumination and realize accurate color reproduction.
However, the above-described conventional color management apparatus has the following problems yet to be solved.
First, there is no means for controlling targets of color reproduction. A target of color reproduction is a target to control colorimetric value XYZ of an image to be reproduced by a display apparatus and there are as many types of color reproduction targets as combinations of types of spectral distribution of illumination of (Mathematical expression 1) and color matching function. For example, when the spectral distribution of illumination on the image capturing side is used as spectral distribution Eλ of illumination and a CIE1931 color matching function specified by the CIE (International Commission of Illumination) is used as the color matching function (x′λ, y′λ, Z′λ), the colorimetric value XYZ calculated expresses colors of an object viewed by a CIE standard observer in image capturing illumination. Then, the target of color reproduction is to “reproduce colors when a CIE standard observer views an object in image capturing illumination”. In this case, the color management apparatus needs to give the display apparatus an image signal that allows the display apparatus to display the “colors of an object viewed by a CIE standard observer in image capturing illumination”.
On the other hand, when the spectral distribution of illumination on the observing side is used as spectral distribution Eλ of illumination and a CIE1931 color matching function specified by the CIE is used as the color matching function (x′λ, y′λ, z′λ), the colorimetric value XYZ calculated expresses colors of an object viewed by a CIE standard observer in observation illumination. Then, the target of color reproduction is to “reproduce colors when a CIE standard observer views an object in observation illumination”. In this case, the color management apparatus needs to give the display apparatus an image signal that allows the display apparatus to display the “colors of an object viewed by a CIE standard observer in observation illumination”.
When the spectral distribution of illumination on the image capturing side differs from the spectral distribution of illumination on the observing side, the colorimetric value XYZ which becomes the target for control of the display apparatus is different. Thus, the image reproduced on the display apparatus has different colors.
The above problem is the one pointed out by the above-described conventional example. Furthermore, the Unexamined Japanese Patent Publication No.HEI 11-85952 discloses the means applicable to two targets of color reproduction by the image capturing side and receiving side having their respective spectral distributions of illumination.
However, the Unexamined Japanese Patent Publication No. HEI 11-85952 does not disclose how this target of color reproduction is determined, that is, the means for controlling the target of color reproduction and lacks a mechanism where by the image capturing side and the observing side can be connected without discrepancy so as to be flexibly applicable to the target of reproduction of a plurality of colors. That is, since there is no “protocol” that connects the image capturing side (color information transmitting side) and observing side (color information receiving side) over a network, there is a problem that a color reproduction intention cannot be exchanged appropriately between the image capturing side and the observing side.
For example, when the observing side sets “reproducing colors of an object viewed from a CIE standard observer in image capturing illumination” as the target of color reproduction, the observing side requests the image capturing side to send the spectral distribution of illumination for image capturing. However, when the image capturing side sets a target of color reproduction different from that of the observing side and sets “reproducing colors of an object viewed from a CIE standard observer in illumination of observation” as a target of color reproduction, spectral distribution Eλ of illumination of (Mathematical expression 1) becomes illumination for observation. For this reason, the image capturing side has no intention to send the spectral distribution of illumination for image capturing to the observing side. This is an example of harmful effects when a common target for color reproduction is not set between the image capturing side and receiving side.
Furthermore, a target of color reproduction is defined in a variety of ways not only from the spectral distribution of illumination but also from differences in the color matching function. Thus, management of a target of color reproduction is a more important issue.
For example, when five observers have color matching functions differing from one another, there are five types of color matching function (x′λ, y′λ, Z′λ) of (Mathematical expression 1). Thus, there are five sets of colorimetric value XYZ as the targets of the display apparatus. Since an infinite number of color reproduction targets are theoretically conceivable, it is impossible to design color reproduction unless a common target is set beforehand between the image capturing side and the observing side.
Second, there is no means for managing task assignment of color reproduction. Task assignment of color reproduction refers to assignment of different types of processing such as calculation of colorimetric value XYZ, estimation of spectral reflectance of images captured and colorimetric control of the display apparatus to different processing sections of the color management apparatus.
For example, when the image capturing side assumes all responsibility for color reproduction and executes all of estimation of spectral reflectance of images captured, calculation of colorimetric value XYZ and calculation of signals for the display apparatus, the image capturing side needs to send the colorimetric device characteristic of the display apparatus to the image capturing side. The image capturing side keeps track of the characteristic of the display apparatus, sends an image signal optimized for the display apparatus to the observing side and the observing side displays the image without applying colorimetric processing, and the target of color reproduction is achieved in this way.
On the contrary, when the observing side assumes all responsibility for color reproduction and executes all colorimetric processing, the output signal of the image capturing apparatus is directly sent to the observing side without being subjected to colorimetric processing. Then, the receiving side performs all processing of estimation of spectral reflectance of images captured, calculation of colorimetric value XYZ and calculation of all signals for the display apparatus and the target of color reproduction is achieved in this way.
Thus, the above-described conventional color management apparatus has a fixed process of colorimetric processing and is not constructed in such away as to flexibly assign a variety of tasks of color reproduction between the transmitting side and receiving side.
Third, there is no means for managing task assignment of color reproduction according to a target of color reproduction. This is a problem that combines the above-described first and second problems. That is, unless the image capturing side and the observing side have a common target for color reproduction, it is impossible to assign tasks of color reproduction between the image capturing side and the observing side and the color management apparatus does not function correctly. For color management that realizes accurate color reproduction, the color reproduction target should be checked between the image capturing side and the observing side and task assignment of color reproduction should be performed between the image capturing side and the observing side. However, the above-described conventional color management apparatus has no means for checking the color reproduction target with each other and has a fixed process of colorimetric processing. For this reason, the conventional color management apparatus is not constructed to flexibly meet a variety of color reproduction targets and color reproduction tasks assigned according to the color reproduction targets.